Core barrel and core drilling systems and methods

ABSTRACT

Example embodiments provide downhole apparatus and methods for wireline core drilling. Example apparatus comprises an outer tube having at least one helical groove formed in an outer surface of the outer tube. The apparatus may also comprise an inner tube for collecting a core sample. The inner tube may be received within a bore of the outer tube. The inner tube and the core sample may be retrieved to a surface by a wireline.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. application No. 63/128,701 filed 21 Dec. 2020 and entitled CORE BARREL AND CORE DRILLING SYSTEMS AND METHODS which is hereby incorporated herein by reference for all purposes. For purposes of the United States of America, this application claims the benefit under 35 U.S.C. § 119 of U.S. application No. 63/128,701 filed 21 Dec. 2020 and entitled CORE BARREL AND CORE DRILLING SYSTEMS AND METHODS.

FIELD

The present disclosure relates to core barrels and deep core drilling systems and methods. Some embodiments provide systems and methods for maintaining a straight line drilling path.

BACKGROUND

Prior to commencing mining operations of a site, it is advantageous to sample ground formations of the site to confirm the presence and/or location of a desired mineral, element, etc.

To sample ground formations, the ground formations may be drilled to obtain core samples of the ground formations. The core samples may then be analyzed. Core samples are often obtained from deep boreholes, for example at depths of 100 m or more or 500 m or more or 1000 m or more.

Drilling operations which are deeper have a higher likelihood of deviating from their intended drill paths. Prior art methods have attempted to reduce the likelihood of the drilling operation deviating from its intended path by using core barrels having an outer tube with four flat sides. However, such outer tubes are prone to getting stuck between drilling cycles (e.g. while a core sample is being retrieved to the surface). A wall of the drilled hole may collapse against the flat side(s) of the outer tube making it impossible to rotate the outer tube.

There is a general need for improved core barrels and core drilling systems.

SUMMARY

Further aspects and example embodiments are illustrated in the accompanying drawings and/or described in the following description.

This invention has many aspects. These include (non-limiting):

-   -   core barrel assemblies;     -   outer tubes and outer tube assemblies for core barrels;     -   systems and methods for maintaining a straight line drilling         path;     -   systems and methods for efficiently extracting core samples;     -   etc.

One aspect of the technology described herein provides a downhole apparatus for wireline core drilling. The downhole apparatus comprises an outer tube having at least one helical groove formed in an outer surface of the outer tube. The downhole apparatus also comprises an inner tube for collecting a core sample. The inner tube is receivable within a bore of the outer tube. The inner tube and the core sample are retrievable to a surface by a wireline.

In some embodiments the outer tube comprises two or more shorter tubes.

In some embodiments the outer tube is at least 2 m long.

In some embodiments the at least one helical groove has a depth that is less than about 0.15 cm.

In some embodiments the at least one helical groove has a width that is less than about 2 cm.

In some embodiments the at least one helical groove is formed on an angle in the range of about 10° to about 20°. In some embodiments the angle is about 15°.

In some embodiments the at least one helical groove makes at least 4 full rotations around the outer tube over an entire length of the outer tube.

In some embodiments the at least one helical groove has a depth that is less than 15% of a wall thickness of the outer tube.

In some embodiments the at least one helical groove is a multi-start helical grove having at least 3 starts or at least 4 starts.

In some embodiments the outer tube comprises a first shorter tube having a first set of helical grooves and a second shorter tube having a second set of helical grooves. The first and second shorter tubes may be coupled together.

In some embodiments coupling the first and second shorter tubes together aligns the first set of helical grooves with the second set of helical grooves.

In some embodiments at least one of the first and second shorter tubes comprises a circumferential gap. The circumferential gap may allow for flow of fluid between the first and second sets of helical grooves when the first and second shorter tubes are coupled together.

In some embodiments the first and second shorter tubes are coupled together with a threaded coupling.

In some embodiments an outer diameter of the outer tube is substantially equal to an inner diameter of a drilled hole. In some embodiments a difference between the outer diameter of the outer tube and the inner diameter of the drilled hole is about 1 mm or less.

In some embodiments the outer tube comprises 4130 alloy steel.

Another aspect of the technology described herein provides an outer tube for a core barrel for wireline core drilling. The outer tube comprises at least one helical groove formed in an outer surface of the outer tube. The outer tube also comprises a bore to receive an inner tube for collecting a core sample. The inner tube and the core sample are retrievable to a surface by a wireline.

In some embodiments the outer tube has one or more features as described herein.

It is emphasized that the invention relates to all combinations of the above features, even if these are recited in different claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate non-limiting example embodiments of the invention.

FIG. 1 is a schematic illustration of a deep core drilling system according to an example embodiment of the invention.

FIG. 2A is a schematic illustration of an outer tube of a core barrel according to an example embodiment of the invention.

FIG. 2B is a cross-sectional view of the outer tube of FIG. 2A.

FIG. 2C is a cross-sectional view of the outer tube of FIG. 2A placed within a hole drilled in a ground formation.

FIG. 3 is a schematic illustration of a deep core drilling system according to an example embodiment of the invention.

FIG. 4 is an exploded assembly view of a core barrel according to an example embodiment of the invention.

DETAILED DESCRIPTION

Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive sense.

FIG. 1 schematically shows an example drilling system 10 operable to drill desired ground formations to acquire deep core samples of the ground formations. For example, it may be desirable to establish and/or locate the presence of minerals (e.g. gold, copper, iron, etc.) in a ground formation prior to undertaking expensive mining operations of the ground formation. Acquired core samples may be studied by a geologist to confirm the presence of a desired mineral.

Drill rig 11 rotates and advances drill string 12 into the ground to form hole 13. Drill string 12 comprises a downhole drilling assembly 14 and a plurality of drill rods which rotatably couple drilling assembly 14 to drill rig 11. Drill rig 11 may, for example, comprise a commercially available surface drill rig such as those manufactured by Boart Longyear™ of Salt Lake City, Utah, USA. Drill rods 15 transfer torque, feed, force and/or rotation speed from drill rig 11 to drilling assembly 14. A length of drill string 12 may be extended by adding drill rods 15. In some applications drill string 12 may be up to 1000 m, 2000 m, 3000 m, 3500 m or 4000 m long.

Drilling assembly 14 comprises a drill bit 16 for cutting the ground formation and an outer tube 17 and an inner tube 18. Inner tube 18 is located within a bore of outer tube 17 and may be used for collecting core samples. Outer tube 17 and inner tube 18 may be part of a core barrel assembly designed to collect core samples of the ground formation being drilled (e.g. core barrel 30 described elsewhere herein).

Drill bit 16 is annular. The annular configuration of drill bit 16 facilitates extraction of cylindrical core samples of the ground formation. Cutting surfaces of drill bit 16 may comprise high-strength materials such as diamond, tungsten carbide, etc. The high-strength materials may increase the life of drill bit 16, increase efficiency of the drilling operation, etc. In some embodiments the high-strength materials are impregnated or embedded into the cutting surfaces of drill bit 16.

Outer tube 17 is a generally cylindrical hollow tube coupled between drill rods and drill bit 16. Outer tube 17 houses inner tube 18 which is a hollow tube configured to collect the core samples. In some embodiments inner tube 18 does not rotate when outer tube 17 or drill string 12 rotate. In some such embodiments a head assembly attached to an uphole end of inner tube 18 isolates inner tube 18 from rotating with outer tube 17. Preferably, inner tube 18 extends upwards from drill bit 16.

Typically, drill bit 16 is configured to cut a hole 13 having a diameter that is greater than outer diameters of other components of drill string 12 (e.g. outer tube 17, drill rods 15, etc.). In some embodiments drilling assembly 14 comprises a reaming shell 19 coupled between drill bit 16 and outer tube 17. Reaming shell 19 widens (or reams) hole 13 cut by drill bit 16 to a desired diameter. In some embodiments outer surfaces of reaming shell 19 at least partially comprise high-strength materials such as diamond, tungsten carbide, etc. In some embodiments the high-strength materials are impregnated or embedded into the outer surfaces of reaming shell 19. Advantageously, reaming shell 19 may at least partially stabilize drill bit 16 relative to drill string 12 (e.g. reduce the likelihood of “drill bit bounce”, off-axis drill bit variations, etc.).

When drill rig 11 is in an active drilling state (e.g. drill string 12 is rotating and/or downward pressure is applied to drill string 12), drilling fluids are pumped down into drill string 12. The drilling fluids cool drill bit 16 (and the other components of drilling assembly 14) and bring drill cuttings back up to the surface.

However, as drill string 12 gets longer drill string 12 becomes more flexible and the likelihood of drilling assembly 14 unintentionally deviating off-axis (i.e. no longer following a straight line drill path) increases. Having drill string 12 deviate from an intended drill path may impact the accuracy of logged locations associated with obtained core samples, cause an incorrect region of the ground formation to be sampled, etc.

Without being limited to any particular theory of operation, the inventor has discovered that the likelihood of drill string 12 deviating from its intended drill path may be reduced by increasing an outer diameter of outer tube 17. The inventor has further discovered that adding helical grooves to an outer surface of outer tube 17 reduces the likelihood of outer tube 17 and drilling assembly 14 getting stuck (i.e. unable to rotate) within hole 13.

FIGS. 2A and 2B are a schematic view and a cross-sectional view respectively of an example outer tube 17. FIG. 2C is a schematic cross-sectional view of outer tube 17 within hole 13. In FIGS. 2B and 2C the depth of helical grooves 17A has been exaggerated for illustration purposes. Although FIGS. 2B and 2C show both outer tube 17 and inner tube 18, outer tube 17 and inner tube 18 are separate components that may be supplied individually.

In some embodiments an outer diameter of outer tube 17 is a closer fit within hole 13 than many commercially available core barrels. In some embodiments the outer diameter of outer tube 17 is generally equal to a diameter of hole 13 with sufficient clearance to allow outer tube 17 to rotate in hole 13. The close fit between outer tube 17 and the inner wall of hole 13 helps to keep drill bit 16 oriented to extend hole 13 along a straight line trajectory.

In some embodiments outer tube 17 has an outer diameter that is about 20 thou (or thousandths of an inch) (about 0.5 mm) to about 40 thou (about 1 mm) less than the diameter of hole 13. In some embodiments outer tube 17 has an outer diameter that is about 20 thou (about 0.5 mm) to about 40 thou (about 1 mm) less than the diameter of reaming shell 19.

Since outer tube 17 may have an outer diameter that extends to match the diameter of hole 13, a wall of outer tube 17 may be thicker than it could otherwise be. Having a thicker wall makes outer tube 17 more rigid thereby reducing the likelihood that outer tube 17 will flex (or bend) and thereby reducing the likelihood that drilling assembly 14 will deviate from its intended drilling path. Additionally, or alternatively, having an outer tube 17 with a larger outer diameter reduces the size of a gap between a wall of hole 13 and the outer surface of outer tube 17 thereby reducing an amount of space in which outer tube 17 can flex (or bend) and thereby reducing the likelihood that drilling assembly 14 will deviate from its intended drilling path.

Additionally, outer tube 17 comprises one or more (and typically a plurality of) helical groves 17A formed into an outer surface of outer tube 17. Helical grooves 17A permit water or other fluids (e.g. drilling fluid) to pass along the outer surface of outer tube 17. Advantageously, rocks, clay or other matter that may enter helical grooves 17A can readily be cleared from helical grooves 17A thereby reducing the likelihood that outer tube 17 (and drilling assembly 14 generally) will become stuck within hole 13 (e.g. if surrounding material of hole 13 was to collapse against outer tube 17). Rotation of outer tube 17 in combination with the configuration of helical groves 17A assists with clearing matter from helical groves 17A and preventing outer tube 17 from becoming stuck. For the purposes herein, “stuck” means that it is no longer possible for drill rig 11 to resume rotation of drill string 12 or drill bit 16 under normal/standard operating circumstances.

In some embodiments outer tube 17 comprises 10 or fewer helical grooves 17A. In some embodiments outer tube 17 comprises 5 or fewer helical grooves 17A.

In some embodiments outer tube 17 has an outer diameter in the range of about 2 inches (about 5 cm) to about 5 inches (about 13 cm).

In some embodiments outer tube 17 has an inner diameter in the range of about 1.5 inches (about 3.8 cm) to about 4.5 inches (about 11.4 cm).

In some embodiments the difference between the outer diameter of outer tube 17 and the inner diameter of outer tube 17 is in the range of about 0.5 inches (about 1.25 cm) to about 0.8 inches (about 2 cm).

In some embodiments helical grooves 17A are formed on an angle (e.g. angle shown in FIG. 2A) in the range of about 10° to 20°. In some embodiments helical grooves 17A are formed on an angle of 15°.

In some embodiments adjacent helical grooves 17A are circumferentially spaced apart from one another by about 40° to about 90°. In some embodiments adjacent helical grooves 17A are circumferentially spaced apart from one another by about 60°. In some embodiments helical groves 17A are equally spaced apart circumferentially. For example, if outer tube 17 comprises 6 helical grooves 17A, each of the helical grooves may be equally circumferentially spaced apart from one another by 60°.

In some embodiments helical grooves 17A extend circumferentially by about to about 0.7° per mm of length of outer tube 17. In some embodiments helical grooves 17A extend circumferentially by about 0.55° per mm of length of outer tube 17.

In some embodiments helical grooves 17A have a depth in the range of about inches (about 0.1 cm) to about 0.06 inches (about 0.15 cm). In some embodiments helical grooves 17A have a width of about 0.75 inches (about 2 cm).

In some embodiments the depth of helical grooves 17A is at most 15% of the overall thickness of the wall of outer tube 17. In some embodiments the depth of helical grooves 17A is at most 10% of the overall thickness of the wall of outer tube 17. In some embodiments the depth of helical grooves 17A is at most 5% of the overall thickness of the wall of outer tube 17. In some embodiments the depth of helical grooves 17A is at most 1% of the overall thickness of the wall of outer tube 17.

Some non-limiting example embodiments of outer tube 17 include:

-   -   an outer diameter of 2.340 inches and an inner diameter of 1.810         inches with 4 helical grooves 17A (may be used to drill to         depths up to about 3,500 m);     -   an outer diameter of 2.965 inches and an inner diameter of 2.380         inches with 6 helical grooves 17A (may be used to drill to         depths up to about 3,000 m);     -   an outer diameter of 3.760 inches and an inner diameter of 3.065         inches with 7 helical grooves 17A (may be used to drill to         depths up to about 2,000 m);     -   an outer diameter of 4.807 inches and an inner diameter of 4.055         inches with 8 helical grooves 17A (may be used to drill to         depths up to about 1,000 m);     -   etc.

Outer tube 17 may be made of steel. In some embodiments outer tube 17 is made of an alloy steel such as 4130 alloy steel.

Outer tube 17 may be machined. Machining outer tube 17 may facilitate more precise manufacturing of outer tube 17 (and helical grooves 17A) compared to other methods of manufacture such as metal forming, etc.

In some embodiments outer tube 17 comprises a plurality of shorter tubes joined together to form outer tube 17. In some embodiments the shorter tubes are joined together with threaded couplings. Outer tube 17 may, for example, comprise two shorter tubes (e.g. shorter tubes 17-1 and 17-2 shown in FIGS. 2A and 3 ). Each of the shorter tubes may be of the same length or of different lengths. Preferably, the couplings which join the shorter tubes together (e.g. threaded couplings) are configured to align helical threads 17A between the shorter tubes such that the helical threads are continuous across the joints between the shorter tubes when the shorter tubes are coupled together. If helical threads 17A cannot be aligned between the shorter tubes, a circumferential gap may be formed in an end of at least one of the shorter tubes being joined together to allow for the passage of fluid from a first set of helical grooves 17A on a first one of the shorter tubes (e.g. shorter tube 17-1) to a second set of helical grooves 17A on a second one of the shorter tubes (e.g. shorter tube 17-2).

Different portions of outer tube 17 may wear out unevenly (e.g. one portion of outer tube 17 may wear out more than another portion of outer tube 17). Having an outer tube 17 which comprises a plurality of shorter tubes advantageously allows individual ones of the shorter tubes to be replaced at different times. For example, a section of outer tube 17 that is worn out may be remediated by replacing the shorter tube which corresponds to that section without having to replace outer tube 17 in its entirety.

In some cases it is advantageous to have outer tube 17 comprise a plurality of shorter tubes to simplify manufacturing of outer tube 17. For example, it may be simpler in some cases to manufacture shorter tubes and helical groves 17A over the shorter length then manufacturing a single longer outer tube 17.

In some embodiments outer tube 17 is at least 2 m long. In some such embodiments outer tube 17 may comprise two shorter tubes (e.g. tubes 17-1 and 17-2) which are each at least 1 m long. In some embodiments outer tube 17 is at least 3 m long. In some such embodiments outer tube 17 may comprise two shorter tubes (e.g. tubes 17-1 and 17-2) which are each at least 1.5 m long.

In some embodiments each helical grove 17A makes at least 3 to 10 full rotations around the total length of outer tube 17. In some embodiments each helical grove 17A makes at least 6 full rotations around the total length of outer tube 17.

To collect core samples, drill string 12 is advanced until inner tube 18 is filled with a core sample (i.e. drill string 12 can advance up to an amount equal to the length of inner tube 18). Inner tube 18 is then retrieved to retrieve the core sample. Inner tube 18 may be replaced and drilling may resume (i.e. drill string 12 continues to be advanced). In some embodiments inner tube 18 is replaced with a clean and/or lubricated inner tube 18. The same inner tube 18 may be re-used or a new inner tube 18 may be used. Typically, after each drilling cycle (i.e. advancement of drill string 12, retrieval of inner tube 18 and replacement of inner tube 18), hole 13 is extended by a length equal to the length of inner tube 18 (or outer tube 17 if the length of outer tube 17 is the same as the length of inner tube 18).

In some embodiments inner tube 18 is retrieved from drill string 12 by recovering all of drill string 12 from hole 13. In such embodiments, drill string 12 is retrieved uphole to the surface component-by-component until outer tube 17 and inner tube 18 are recovered from hole 13. To advance drilling again, the components of drill string 12 must be returned downhole into hole 13. This may be very time intensive, laborious, expensive and slow.

In some embodiments inner tube 18 is retrieved using a wireline 20 (see e.g. FIG. 3 ). A head assembly 21 may be coupled to an uphole end of inner tube 18. Head assembly 21 may comprise a locking assembly comprising one or more features which engage one or more corresponding features of outer tube 17 (or drill string 12) to lock a position of inner tube 18 relative to outer tube 17. In some embodiments an adaptor coupling 22 and locking coupling 23 are coupled between outer tube 17 and drill rods 15. In some embodiments features of the locking assembly of head assembly 21 engage one or more corresponding features of one or both of adapter coupling 22 and locking coupling 23. In some embodiments head assembly 21 comprises two or more latches 24 which are received within corresponding recesses of adaptor coupling 22. A bottom of locking coupling 23 may retain latches 24 within the recesses of adaptor coupling 22 to axially retain inner tube 18 relative to outer tube 17.

An overshot 26 may be coupled to a downhole end of wireline 20. Overshot 26 may be lowered downhole and positioned to receive head assembly 21 to release inner tube 18 from outer tube 17 (i.e. release the locking assembly of head assembly 21) and to couple inner tube 18 to wireline 20. Retrieving wireline 20 while inner tube 18 is coupled also retrieves inner tube 18 (and a collected core sample) uphole to the surface.

To resume drilling, a replacement inner tube 18 as described elsewhere herein (e.g. the same inner tube 18 which will be re-used or a new inner tube 18) may be lowered using wireline 20. In some embodiments the locking mechanism of head assembly 21 automatically engages corresponding features of outer tube 17 (or adaptor coupling 22 and/or locking coupling 23, or other components of drill string 12) once inner tube is lowered down to its resting position within outer tube 17.

FIG. 4 is an exploded assembly view of an example core barrel 30 (e.g. an assembly including outer tube 17 and inner tube 18) for recovering a core sample.

Inner tube 18, head assembly 21 and core case 32 are received within a bore extending through outer tube 17 (and optionally one or more of drill bit 16, reaming shell 19, adaptor coupling 22 and locking coupling 23). As shown in FIG. 4 , components of core barrel 30 may be coupled together using threaded couplings.

In some embodiments a stabilizer 35 is included between reaming shell 19 and outer tube 17. Stabilizer 35 assists with keeping inner tube 18 centered relative to outer tube 17 and drill string 12. Additionally, or alternatively, stabilizer 35 stabilizes inner tube 18 within reaming shell 19 and/or drill bit 16. In some embodiments a landing ring 36 is included between outer tube 17 and adaptor coupling 22 to provide a landing area for inner tube 18 (and/or head assembly 21).

In some embodiments core case 32, a core lifter 33 and a stop ring 34 are coupled to a downhole end of inner tube 18. Core case 32, core lifter 33 and stop ring 34 assist with holding a core sample within inner tube 18 and with breaking off the core sample from the ground formation when it is time to retrieve the core sample. Core lifter 33 allows a core sample to enter into the cavity of inner tube 18 while drill string 12 is actively drilling. Once inner tube 18 is full (or drill string 12 is no longer advanced) core lifter 33 firmly grips the core sample. Stop ring 34 provides a surface for core lifter 33 to bear against (e.g. prevents core lifter 33 from being forced into the cavity of inner tube 18). Core case 32 houses core lifter 33 and stop ring 34 while allowing drilling fluid to flow past inner tube 18 to drill bit 16.

Using wireline 20 to retrieve inner tube 18 and thereby the core sample advantageously permits other components of drill string 12 to remain downhole within hole 13 (i.e. the whole drill string 12 does not have to be retrieved and reassembled every drilling cycle). This increases efficiency of the drilling, makes the drilling faster, reduces costs, etc.

In some embodiments one or more components of drill string 12 comprise helical groves in addition to outer tube 17. In some embodiments one or more of drill bit 16, reaming shell 19, adaptor coupling 22 and locking coupling 23 comprise helical grooves in addition to helical groves 17A of outer tube 17. In some embodiments the additional helical groves of one or more of drill bit 16, reaming shell 19, adaptor coupling 22 and locking coupling 23 are the same as helical groves 17A of outer tube 17 however this is not necessary. In some embodiments one or more of the components (e.g. one or more of drill bit 16, remaining shell 19, adaptor coupling 22, locking coupling 23, etc.) are manufactured for the helical groves of the components to align with one another and/or with helical groves 17A. In some embodiments one or more of the components (e.g. one or more of drill bit 16, remaining shell 19, adaptor coupling 22, locking coupling 23, etc.) comprise circumferential gaps which allow for passage of fluids between adjacent sets of helical groves even if the sets of helical groves are not aligned with one another.

A retrieved core may be stored in, for example, a core box. A record of the exact location of the drilling corresponding to the core may be kept. The record may also comprise date information, time information, depth information, any losses that occurred during core recovery, etc. The record may, for example, assist a geologist when analyzing a retrieved core sample.

In some embodiments the drilling fluid may assist with recovery of a core sample. For example, additives in the drilling fluid may at least partially solidify a core sample, stabilize hole 13, lubricate components of drill string 12, reduce torque that must be applied by drill rig 11 on drill string 12, prevent rust of components of drill string 12, etc.

Interpretation of Terms

Unless the context clearly requires otherwise, throughout the description and the claims:

-   -   “comprise”, “comprising”, and the like are to be construed in an         inclusive sense, as opposed to an exclusive or exhaustive sense;         that is to say, in the sense of “including, but not limited to”;     -   “connected”, “coupled”, or any variant thereof, means any         connection or coupling, either direct or indirect, between two         or more elements; the coupling or connection between the         elements can be physical, logical, or a combination thereof;     -   “herein”, “above”, “below”, and words of similar import, when         used to describe this specification, shall refer to this         specification as a whole, and not to any particular portions of         this specification;     -   “or”, in reference to a list of two or more items, covers all of         the following interpretations of the word: any of the items in         the list, all of the items in the list, and any combination of         the items in the list;     -   the singular forms “a”, “an”, and “the” also include the meaning         of any appropriate plural forms.

Words that indicate directions such as “vertical”, “transverse”, “horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”, “outward”, “left”, “right”, “front”, “back”, “top”, “bottom”, “below”, “above”, “under”, and the like, used in this description and any accompanying claims (where present), depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

For example, while processes or blocks are presented in a given order, alternative examples may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified to provide alternative or subcombinations. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, or may be performed at different times.

In addition, while elements are at times shown as being performed sequentially, they may instead be performed simultaneously or in different sequences. It is therefore intended that the following claims are interpreted to include all such variations as are within their intended scope.

Where a component (e.g. a drill bit, outer tube, inner tube, etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.

Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments.

Various features are described herein as being present in “some embodiments”. Such features are not mandatory and may not be present in all embodiments. Embodiments of the invention may include zero, any one or any combination of two or more of such features. All possible combinations of such features are contemplated by this disclosure even where such features are shown in different drawings and/or described in different sections or paragraphs. This is limited only to the extent that certain ones of such features are incompatible with other ones of such features in the sense that it would be impossible for a person of ordinary skill in the art to construct a practical embodiment that combines such incompatible features. Consequently, the description that “some embodiments” possess feature A and “some embodiments” possess feature B should be interpreted as an express indication that the inventors also contemplate embodiments which combine features A and B (unless the description states otherwise or features A and B are fundamentally incompatible).

It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, omissions, and sub-combinations as may reasonably be inferred. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole. 

1. Downhole apparatus for wireline core drilling comprising: an outer tube having at least one helical groove formed in an outer surface of the outer tube; and an inner tube for collecting a core sample, the inner tube receivable within a bore of the outer tube, the inner tube and the core sample retrievable to a surface by a wireline.
 2. The apparatus of claim 1 wherein the outer tube comprises two or more shorter tubes.
 3. The apparatus of claim 1 wherein the outer tube is at least 2 m long.
 4. The apparatus of claim 1 wherein the at least one helical groove has a depth that is less than about 0.15 cm.
 5. The apparatus of claim 1 wherein the at least one helical groove has a width that is less than about 2 cm.
 6. The apparatus of claim 1 wherein the at least one helical groove is formed on an angle in the range of about 10° to about 20°.
 7. The apparatus of claim 6 wherein the angle is about 15°.
 8. The apparatus of claim 1 wherein the at least one helical groove makes at least 4 full rotations around the outer tube over an entire length of the outer tube.
 9. The apparatus of claim 1 wherein the at least one helical groove has a depth that is less than 15% of a wall thickness of the outer tube.
 10. The apparatus of claim 1 wherein the at least one helical groove is a multi-start helical grove having at least 4 starts.
 11. The apparatus of claim 2 wherein the outer tube comprises a first shorter tube having a first set of helical grooves and a second shorter tube having a second set of helical grooves, the first and second shorter tubes coupled together.
 12. The apparatus of claim 11 wherein coupling the first and second shorter tubes together aligns the first set of helical grooves with the second set of helical grooves.
 13. The apparatus of claim 11 wherein at least one of the first and second shorter tubes comprises a circumferential gap, the circumferential gap allowing for flow of fluid between the first and second sets of helical grooves when the first and second shorter tubes are coupled together.
 14. The apparatus of claim 11 wherein the first and second shorter tubes are coupled together with a threaded coupling.
 15. The apparatus of claim 1 wherein an outer diameter of the outer tube is substantially equal to an inner diameter of a drilled hole.
 16. The apparatus of claim 15 wherein a difference between the outer diameter of the outer tube and the inner diameter of the drilled hole is about 1 mm or less.
 17. The apparatus of claim 1 wherein the outer tube comprises 4130 alloy steel.
 18. An outer tube for a core barrel for deep wireline core drilling comprising at least one helical groove formed in an outer surface of the outer tube, the outer tube comprising a bore to receive an inner tube for collecting a core sample, the inner tube and the core sample retrievable to a surface by a wireline. 19.-21. (canceled) 